1. Field of the Invention
The present invention relates to a liquid crystal display apparatus and a liquid crystal television.
2. Description of the Related Art
In a liquid crystal display apparatus such as a liquid crystal television, performing of gamma correction in such a manner to cause a drive voltage-transmissivity characteristic to become linear is common. However, in such general gamma correction, if the brightness average value level of a video signal is inclined to either a high level or a low level, there is a problem that the variable range of a brightness level becomes narrower and the contrast of a display screen is decreased. It has been known that, in order to solve such a problem, the gamma correction is dynamically performed according to a brightness average level (for example, Japanese Patent Application Laid-Open No. Hei 6-6820).
Further, it has also been known that, as a technology for dynamically performing the gamma correction, gamma correction data is used properly according to atmospheric illumination of the exterior of a display apparatus (for example, Japanese Patent Application Laid-Open No. Hei 11-234539).
Incidentally, in the liquid crystal display apparatus including the liquid crystal television, the transmissivity of backlight is adjusted by controlling the aperture factor of liquid crystal cells, whereby the brightness of respective pixels are determined. Therefore, as well known, even if the aperture factor of the liquid crystal cells is reduced to a minimum, the liquid crystal cells can not perfectly interrupt the transmission of the backlight and can not perform complete black display. Because of such a physical limitation, even if the dynamic gamma correction that has been discussed above is performed, there is a limit to improvement in contrast on the low brightness side (in the vicinity of 0% luminous intensity).
On the other hand, there is also a technology for saving electricity by recognizing a non-displaying region of a liquid crystal panel and controlling the supply of electric power to lamps corresponding to the recognized non-displaying region (for example, Japanese Patent Application Laid-Open No. 2003-66929). That is, this is a technology where, in a region where one lamp takes charge of light-irradiating, when image display is not performed in all of liquid crystal cells in this region, the lamp is caused to be dimmed. However, although this technology is available for a display apparatus in which display is performed so as to create a positive division of lightness and darkness on its screen, it is not suitable for a display apparatus which displays motion pictures such as movie, drama. That is, in such a display apparatus, a continuous image is displayed over the entire screen, so that it is difficult to set the region. If improvement of contrast in an image in which a brightness distribution is inclined is realized by utilizing the technology disclosed in Japanese Patent Application Laid-Open No. 2003-66929, brightness must be monitored at a level at the vicinity of pixels and processing amount becomes enormous.